Explanatory notes to the digital geological map of the Rax ... - KATER

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KATER II Geology of the Rax-Schneeberg-region __________________________________________________________________________________________ Fig. 4: Tectonic sketch of the south-eastern part of the NCA. 19
KATER II Geology of the Rax-Schneeberg-region __________________________________________________________________________________________ Contemporaneous compressional tectonics has affected the Tethyan Ocean and the adjacent shelf of the Austroalpine realm, causing the first displacements of the Juvavic Nappe System. The concept of Jurassic gravitational nappe movements, which was developed in the central NCA, seems to be also useful in the eastern NCA - see TOLLMANN 1987. The stratigraphic sequence of the Göller nappe ends with the Jurassic Allgäu Formation and red limestones and chert and dips down below the Schneeberg Nappe, also visible in the Hengst- and Ödenhof Window. Unfortunately transgressiv Upper Jurassic sediments, sealing the Jurassic movements like in the Salzkammergut, or Lower Cretaceous syntectonic clastics are not preserved. Therefore the Jurassic or Early Cretaceous age of the oldest transversal movements cannot be proven directly. Subduction processes at the southern margin of the Penninic Ocean have started during the Early Cretaceous, accompanied by heating and crustal shortening within the Austroalpine crystalline basement and by wide spread synorogenic clastics and thrust movements in its sedimentary cover, forming the Bajuvaric, Tyrolic and Noric Nappe Systems - DECKER et al. 1987, FAUPL & WAGREICH 2000. For details of metamorphic evolution of the Eastern Alps and controversial discussions see FRANK 1987. Apart from slightly metamorphosed beds at the basal parts - mainly within the siliciclastic Permoscythian rocks - it was assumed that most parts of the NCA do not exhibit any metamorphic overprint - see KRALIK et al. 1987. Investigations of Conodont Color Alteration Index during the last years have revealed a considerable thermal event in parts of the Juvavic nappes, predating the oldest (presumed Late Jurassic) transversal movements - GAWLICK et al. 1994, KOZUR & MOSTLER 1992 , MANDL 1996. Upper Cretaceous clastic sediments of the Gosau-Group transgressed after a periode of erosion over the NCA nappe stack. The sediments of the Gosau-Group show a facies change in time from shallow water clastics to flysch-like deep water sediments, WAGREICH & FAUPL 1994. The latter ones are also typical for the adjacent Penninic trough, where beside other structural units (e.g. ophiolite-bearing metamorphic Bündnerschiefer-Group of the Tauern-Window) the Rhenodanubian Flysch Zone originates from. Ongoing subduction of the Penninic realm toward the south below the Austroalpine units led to the closure of the Penninic Ocean. The sediments of the Rhenodanubian Flyschzone became deformed, lost their oceanic basement (only preserved in form of some Klippen) and became partly overthrusted by the nappes of the NCA, beginning in the late Eocene. This tectonic event is responsible for reactivation of older thrusts within the NCA, causing an incorporation of Gosau Group rocks into the nappe stack by local thrusting toward the north as well as backthrusting toward the south. The remaining sea between the alpine orogenic front and the European foreland during Oligocene and Early Miocene has been the depositional site of the Molasse Zone, which one collected the erosional debris of the uplifting Alps – see KUHLEMANN & KEMPF 2002. The southernmost part of the Molasse Zone became also incorporated into the alpine orogeny due to the youngest subduction pulses. The uplift of the central part of the Eastern Alps during Miocene was accompanied by large strike slip movements on its northern part (sinistral Salzach-Ennstal and Mur-Mürz fault systems; responsible also for the genesis of the Vienna Basin and also affecting the NCA) - see for example LINZER et al. 1995, DECKER et al. 1994. 20
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Explanatory notes to the digital geological map of the Rax ... - KATER

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